Non-volatile memory, system, and method

ABSTRACT

A non volatile memory device includes a first buffer register configured to receive and store the data to be stored into the memory device provided via a memory bus. A command window is activatable for interposing itself for access to a memory matrix between the first buffer element and the memory matrix. The command window includes a second buffer element that stores data stored in or to be stored into a group of memory elements. A first data transfer means executes a first transfer of the data stored in the second buffer register into the first buffer register during a first phase of a data write operation started by the reception of a first command. A second data transfer means receives the data provided by the memory bus and modifies, based on the received data, the data stored in the first buffer register during a second phase of the data write operation started by the reception of a second command. The first transfer means execute a second transfer of the modified data stored in the first buffer register into the second buffer register during a third phase of the data write operation. The second transfer is executed in response to the reception of a signal received by the memory bus together with the second command.

PRIORITY CLAIM

This application claims priority from Italian patent application No.MI2007A000787 filed Apr. 17, 2007, which is incorporated herein byreference.

TECHNICAL FIELD

Embodiments of the present invention generally relate to the electronicfield. Particularly, embodiments of the present invention relate tonon-volatile memory devices of the Double Data Rate (DDR) type, and tomethods for accessing, particularly for writing, these memories.

BACKGROUND

DDR Synchronous Dynamic Random Access Memories (DDR SDRAMs) are known. ADDR SDRAM is a type of volatile memory that is extensively used assystem memory for the computers, for example for the Personal Computers(PC).

Unlike other types of random access memories, a SDRAM memory is providedwith a synchronous interface. Thus, the SDRAM memory requires thepresence of a clock signal that is used for driving a finite statemachine for timing the instructions received at control inputs of thememory. Thanks to this timing, an SDRAM memory is capable of managingoperations that are more complex compared to those manageable by meansof non-synchronous random access memories, such as a dynamic randomaccess memory (DRAM).

The SDRAM memories are further characterized by having a high potentialaccess band because each reading operation may interest severalthousands of information bits.

For further improving the performances offered by such a memory type, aDouble Data Rate (DDR) interface has been developed. Thanks to thepresence of the double rate interface, the memory is capable ofexecuting two reading or writing transfers for each cycle of the clocksignal (particularly, one in correspondence of the rising fronts of theclock signal, and one in correspondence of the falling fronts). Comparedto the other SDRAM memories, the minimum read/write unit (i.e., theminimum quantity of data that is read/written during an access to thememory) is doubled: in a DDR SDRAM memory, each single access refers toat least two consecutive memory words. This technique allows thedoubling of the transfer speed of the data without having to increasethe working frequency of the memory bus. In other words, the clocksignal of a DDR SDRAM is exploited more with respect to the case of asingle rate SDRAM memory, because the “real” transfer frequency is twicethe clock frequency.

As it is known to the skilled technicians, the Joint Electron DeviceEngineering Council (JEDEC) has established standards regarding thecharacteristics and the specifics of the DDR SDRAMs. Moreover, the JEDEChas provided several specific protocols for the management of theoperations required for the use and operation of such memories.

Seeing the numerous advantageous characteristics of the DDR SDRAMmemories, it would be desirable to have a non-volatile counterpartthereof (capable of maintaining the information even in absence of anelectrical supply), i.e., a Non-Volatile DDR Memory (DDR NVM), to becoupled thereto. In this way, it would be possible to have performancescomparable to that offered by the DDR SDRAM memories in all thoseapplication fields that require the saving of the information in apermanent way, but that, at the same time, require short response times.Moreover, in certain applications in which the available resources,intended as both available power and available silicon area within thechip integrating the memories, are limited, it would be highly desirablethat the DDR SDRAM memories and the DDR NVM memories use the sameinterfaces and the same communication buses as much as possible. Forexample, in order to increment the speed performances of mobileterminals for telecommunications, it would be advantageous to substitutethe non-volatile memories of the classic type used for storing data withDDR NVM memories, reducing the access times to the memory.

A substantial difference occurring between the non-volatile memories andthe volatile memories consists in the different way the data are written(program phase). Particularly, the program phase of a non-volatilememory is usually more complex and requires a higher amount of time. Forexample, in order to program a flash non-volatile memory it is necessaryto apply a series of (voltage or current) pulses to the memory cells tobe programmed, and, after the application of each pulse, the programmingstate of the memory cells is usually verified. This requires a greateramount of time compared to that necessary for programming the samequantity of data in a volatile memory.

Because of the major difference occurring between the DDR NVM memoriesand the DDR SDRAM memories, it would be thus necessary to differentiatethe communication buses and at the same time follow protocols for themanagement of the operations that are greatly different to each others.However, such a solution is expensive in terms of resources, and thusnot optimized to be implemented for mobile terminals fortelecommunication devices (and in general for the devices having limitedresources).

SUMMARY

An embodiment of the present invention proposes a non volatile memorydevice. Such memory device is adapted to be coupled to a memory busadapted to provide data to be stored in the memory device and commandsto be executed by the memory device. The memory device includes a memorymatrix that includes memory elements adapted to memorize or store thedata in a non-volatile way. At least a first buffer register isconfigured to receive and memorize in a volatile way the data to bestored into the memory device provided by the memory bus. A commandwindow is activatable for interposing itself for the access to thememory matrix. Between the at least one first buffer element and thememory matrix, the command window includes at least one second bufferelement adapted to store in a volatile way data stored in or to bestored into a group of memory elements. The memory device furtherincludes first data transfer means adapted to execute a first transferof the data stored in the at least one second buffer register into theat least one first buffer register during a first phase of a data writeoperation in the memory device started by the reception of a firstcommand. A second data transfer means is adapted to receive the dataprovided by the memory bus and to modify, based on the received data,the data stored in the at least one first buffer register during asecond phase of the data write operation started by the reception of asecond command. The first transfer means are adapted to execute a secondtransfer of the modified data stored in the at least one first bufferregister into the at least one second buffer register during a thirdphase of the data write operation, the second transfer being executed inresponse to the reception of a signal received by the memory bustogether with the second command.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, as well as further features and advantages thereofwill be best understood by reference to the following detaileddescription of embodiments thereof, given purely by way of anon-restrictive indication, to be read in conjunction with theaccompanying drawings. In this respect, it is expressly intended thatthe figures are not necessarily drawn to scale and that, unlessotherwise indicated, they are merely intended to conceptually illustratethe structures and procedures described herein. Particularly:

FIG. 1 is a schematic of an electronic system i according to anembodiment of the present invention;

FIG. 2 is a functional block diagram of a DDR NVM memory included in theelectronic system of FIG. 1;

FIG. 3 shows two examples of how the memory space defined by a commandwindow of the DDR NVM memory of FIG. 2 can overlap the memory spacedefined by a memory matrix included in the memory of FIG. 2;

FIG. 4 is a diagram that illustrates the evolution in time of the dataand commands that flow on a memory bus of the DDR NVM memory during awrite operation according to an embodiment of the present invention;

FIG. 5 illustrates a state diagram of the DDR NVM memory according toone embodiment of the present invention; and

FIG. 6 is a timing diagram illustrating the delays of the commandsduring a write operation of the DDR NVM memory.

DETAILED DESCRIPTION

The following discussion is presented to enable a person skilled in theart to make and use the invention. Various modifications to theembodiments will be readily apparent to those skilled in the art, andthe generic principles herein may be applied to other embodiments andapplications without departing from the spirit and scope of the presentinvention. Thus, the present invention is not intended to be limited tothe embodiments shown, but is to be accorded the widest scope consistentwith the principles and features disclosed herein.

With reference to the FIG. 1, several of the main components of anelectronic system 100 according to an embodiment of the presentinvention are schematically illustrated.

The electronic system 100 may be part of a greater system (not shown inthe figure) making for example reference to the field of mobile devicesfor telecommunication the electronic system 100 may be included in acellular phone.

The electronic system 100 includes a processor 110, a volatile memory120 and a non-volatile memory 130. The volatile memory 120 may forexample form the system memory for the operation of the cellular phone,and the non-volatile memory 130 may instead form the mass memory for thestoring of information that need to be maintained even in absence ofpower supply of the cellular phone (for example, the firmware used bythe phone processors, the application programs and the personalinformation of the phone user). The processor 110 is coupled with thevolatile memory 120 and the non-volatile memory 130 by means of a commoncommunication bus 140, in the following referred to as memory bus.Particularly, the memory bus 140 includes a data bus, onto which thedata to be stored into the memories 120, 130 or the data read therefromare sent, and a command and address bus, that is used by the processor110 for providing the addresses for specifying the locations to beaccessed in the memories 120, 130, and the commands that have to beexecuted by the memories.

The volatile memory 120 comprises a DDR SDRAM memory, while thenon-volatile memory 130 comprises a DDR NVM memory, for example a doubledata rate flash memory.

A clock signal CK is generated by the processor 110, and is providedboth to the volatile memory 120 and the non-volatile memory 130 fortiming their operation.

The function of the processor 110 is to control the operations of theelectronic system 100. In particular, the processor 110 includes amemory controller 150 adapted to generate and manage a data, addressesand commands that flow on the memory bus 140 for being sent/received bythe processor 110 and by the memories 120, 130.

The memory controller 150 comprises logic circuits adapted to manage theread and write operations of the DDR SDRAM memory 120 and of the DDRSDRAM memory 130. Furthermore, the memory controller 150 manages therefresh operations of the DDR SDRAM memory 120, necessary formaintaining the data stored therein. Should a constant update of thedata stored in the DDR SDRAM memory 120 not performed, such data wouldbe lost. Indeed, because of the presence of unavoidable leakagecurrents, the memory elements of the DDR SDRAM memory 120, i.e.,capacitors adapted to store electrical quantities depending on thedatum, tend to discharge within a certain time period (according to theJEDEC standards, within 64 milliseconds).

Making now reference to the FIG. 2, the structure of the DDR NVM memory130 is illustrated in greater detail, in terms of functional blocks.

As will be more clear in the following description, some of thesignificant elements that constitute the DDR NVM memory 130 are the samethat are included in the DDR SDRAM memory 120. Thanks to thesesimilarities, exploiting a substantial single protocol for themanagement of the operations of both the memories is possible.

The DDR NVM memory 130 comprises a memory matrix 200, which includesmemory elements adapted to the storing of the data in a non-volatileway. For example, the memory matrix 200 is a matrix of flash memoryelements, whose memory elements comprise floating gate MOS transistorsthat can be programmed by varying the threshold voltage byinjecting/removing electrical charges into/from the floating gate. Forthe purpose of simplifying the present description, it is supposed thatwithin the memory matrix 200 are included not only the memory elements,but also the command circuits that usually are present within anon-volatile memory, such as the decoders, the selectors and the programand reading circuits.

The memory matrix 200 is adapted to receive from the memory bus 140 arow address RADD, and to provide the contents of the memory elements ofthe row of the matrix 200 corresponding to the row address RADD to afirst terminal of a selector 205. In a similar way, the memory matrix200 is adapted to receive data from the first terminal of the selector205, and to memorize them into the memory elements of the row of thememory matrix 200 corresponding to the row address RADD. The selector205 includes a second terminal coupled with a functional block denotedwith the term “command window”, and identified with the reference CW,whose purpose and operation will be described description, The selector205 further comprises a third terminal coupled with an input/outputterminal of a further selector 210 and a control terminal coupled with aselection block 215, which is adapted to receive from the memory bus 140the row address RADD.

Based on the row address RADD, the selection block 215 drives theselector 205 through the control terminal, for establishing a selectiveconnection between the third terminal of the selector 205 and a selectedterminal between the first and second terminals of the selector 205. Inthis way, the selector 205 is operable to selectively connect the memorymatrix 200 or the command window CW with the selector 210 according tothe row address RADD.

The selector 210 includes four further terminals, each one connected toa corresponding volatile row register RDBi (i=0,1,2,3), and a controlterminal, adapted to receive from the memory bus 140 register selectionsignals RDBSEL. According to the register selection signals RDBSELvalues, the selector 210 is capable of selecting a row register RDBi andconnecting it to the input/output terminal (i.e., coupling it with theselector 205). The dimension of each row register RDBi depends on thenumber of memory elements that form the generic row of the memory matrix200: each row register RDBi is in fact capable of memorizing or storingthe information corresponding to all the memory elements of a row of thememory matrix 200.

In a similar manner, each row register RDBi is coupled with acorresponding terminal of a further selector 220, which includes aninput/output terminal connected to a data transfer block 230 and acontrol terminal adapted to receive from the memory bus 140 the registerselection signals RDBSEL. According to the register selection signalsRDBSEL values, the selector 220 is capable of selecting a row registerRDBi and connecting it to the input/output terminal (i.e., coupling itwith the data transfer block 230).

The data transfer block 230 has a terminal connected to the memory bus140 for receiving information from the outside, for example, data to bestored in the memory matrix 200 or for outputting on the memory bus 140information stored in the device, for example, data read from the memorymatrix, and a terminal for receiving a drive signal CSEL generated by afinite state machine 235, which receives the clock signal CK and, fromthe memory bus 140, a column address CADD. The finite state machine 235further comprises a command interface, adapted to receive from thememory bus 140 commands CMD sent by the memory controller 150, andinstruct the various components of the DDR NVM memory 130 according tothe received commands CMD.

According to the operation that the DDR NVM memory 230 is executing, thedata transfer block 230 may receive the content of a row register RDBiselected by the selector 220, and transfer the data onto the memory bus140, or may provide a new content to the selected row register RDBiusing data coming from the memory bus 140. Since each row register RDBiincludes a quantity of data equal to that storable using all the memoryelements of a row of the memory matrix 200, and since a read operationor a write operation generally regards only a portion of such quantity,the transfer of data from the memory bus 140 and the selected rowregister RDBi (and vice versa) is managed by the finite state machine235, which defines for each clock interval which portion(s) of data areto be taken from the selected row register RDBi or to be providedthereto according to the column address CADD and the command CMD.

The operations carried out by the DDR NVM memory 230 during the readingof the data stored in the memory matrix 200 will be described in thefollowing, according to a first reading modality, which does not makeuse of the command window CW.

According to this first modality, the reading operations areadvantageously executed in a way similar to that defined by the JEDECprotocol for the DDR SDRAM memories.

Particularly, the reading operation consists of distinct phases: a firstphase, denoted “row opening phase”, followed by one or more “read accessphases”. The row opening phase is started in response to the sending ofa corresponding command CMD provided by the memory controller 150through the command bus of the memory bus 140, and denoted “ACTIVE”. Inthe same way, each read access phase is started in response to thesending of a corresponding command CMD provided by the memory controller150 through the command bus of the memory bus 140, and denoted “READ”.

During the row opening phase, the row address RADD corresponding to therow of the memory matrix 200 including the memory elements whose contenthas to be read is sent on the memory bus 140. The row address RADD isthus provided both to the memory matrix 200 and to the selection block215. In response to the reception of the row address RADD, the memorymatrix 200 carries out internal reading operations, providing the datastored in the memory elements corresponding to the addressed row to thefirst terminal of the selector 205. Then, the selection block 215 drivesthe selector 205 for selecting the memory matrix 200 (this point will bemore clear in the following description). In this way, the data readfrom the memory matrix 200 are provided to a row register RDBi selectedby means of the register selection signals RDBSEL. The decision on whichrow register RDBi has to be selected is carried out by the memorycontroller 150 The selection rules of the row register RDBi may dependon several factors, such as the quantity of row registers RDBi that havenot yet been used and the possibility of optimizing the memoryperformances as much as possible.

As a consequence, at the end of the row opening phase, the data readfrom the selected row of the memory matrix 200 is stored in the rowregister RDBi selected by the memory controller 150.

Each read access phase consists instead in the transfer of the datapreviously stored in the row register RDBi toward the memory bus 140. Asalready anticipated in the previous, the reading operation regards oneor more portions of the data corresponding to the whole row, where eachportion is identified by a corresponding column address CADD. As aconsequence, during each read access phase, the selector 220 is drivenby means of the register selection signals RDBSEL for providing thecontent of the row register RDBi used in the preceding row opening phaseto the transfer block 230, which outputs the selected portions of thedata on the memory bus 140 according to the column address CADD (bymeans of a proper driving carried out by the finite state machine 235).

The procedure that has been previously described is similar to that usedfor reading data stored in the DDR SDRAM memories. This is possiblebecause the reading times of a non-volatile memory, for example, a flashmemory, may be of the same order of magnitude of those employed by aSDRAM memory.

The presence of more than one row register RDBi allows further speedingup of the reading operations, since it is possible to carry out a readaccess phase using a row register RDBi and at the same time carry out anew row opening phase using another register (in other words, it ispossible to operate according to a “pipelined” mode).

While the reading procedure previously described does not move away fromthat normally used for the reading of the DDR SDRAM memories, the sameconsiderations cannot be applied to the writing.

Indeed, according to the protocol of the DDR SDRAM memories, a writingoperation for a DDR SDRAM is composed by the following phases: a firstrow opening phase, equivalent to that previously described for thereading, followed by one or more phases denoted “write access phase”,and lastly a phase denoted “row closure phase”. Even in that case, therow opening and write access phases are started in response to thesending of corresponding commands CMD provided by the memory controller150 through the command bus of the memory bus 140: particularly, the rowopening phase is started by an “ACTIVE” command, while each write accessphase is started by a corresponding “WRITE” command.

According to an embodiment of the present invention, such protocol,conceived for the DDR SDRAM, is used for interacting with the DDR NVMmemory 130.

During the row opening phase, the data corresponding to the row of thememory matrix 200 selected by means of the row address RADD are storedinto a row register RDBi.

At this point, during each write access phase, portions of said datastored in the row register RDBi are replaced with new data coming fromthe memory bus 140. This operation is managed by the finite statemachine 235 using the column address CADD, in a similar way to thatdescribed for the reading operation.

The last phase, i.e., the row closure phase, comprises transferring thecontent of the row register RDBi, which has been modified during thewrite access phases, to the memory matrix 200, which provides forupdating the data corresponding to the selected row with the content ofthe row register RDBi by means of internal write operations.

According to the protocol of the DDR SDRAM memories, the row closurephase may be activated in two different ways. Particularly, the rowclosure phase may be activated in an explicit way, by means of thesending of a command CMD denoted “PRECHARGE” (i.e., in the same way asfor the row opening and write access operations), or may be activated inan automatic way. For this purpose, it is exploited a predeterminedvalue of a signaling bit, sent together with the last WRITE command.

However, the Applicant has observed that this procedure is not efficientfor the non-volatile memories.

Indeed, supposing that the memory matrix 200 includes memory elements ofthe flash type, the row closure phase would require a high quantity oftime, since the updating of the data corresponding to the selected rowwith the content of the row register RDBi requires the execution of awriting phase composed by many (and expensive, in terms of time)operations (in the case of the flash memories, the applications of anon-negligible number of programming pulses).

Having a row closure phase that is excessively expensive in terms oftime, problems regarding the management of the row registers RDBi mayoccur. Indeed, during a row closure phase that involves a determined rowregister RDBi, it may be necessary to use the same row register RDBi forexecuting a row opening phase of another writing operation (for example,in case the remaining row registers RDBi are occupied). As aconsequence, in order not to prematurely interrupt the row closure phaseof the first operation and not to lose data that are not stilltransferred into the memory matrix 200, all the various schedules shouldbe taken into account in an accurate ways, with a consequent increase inthe complexity of the operations to be managed. In this case, it wouldbe necessary to modify the protocol, and/or add additional controlcircuits.

A further problem that may arise using this writing procedure isconnected to the different granularity that a DDR NVM memory may havewith respect to a DDR SDRAM memory. Indeed, while in a DDR SDRAM memoryit is possible to write data with a granularity of bytes, this isusually not possible for a DDR NVM memory. For example, in a flashmemory the granularity is typically much higher than a single byte,since the modification of even a single data byte may request thepreliminary erasure of a whole memory page. As a consequence, while fora DDR SDRAM it is possible to execute a row closure phase for updating alittle portion of the selected row of the memory matrix 200, for a DDRNVM memory it is necessary to wait until the portion of the row to beupdated is sufficiently large.

For the purpose of resolving the above mentioned problems, during awriting operation on the DDR NVM memory, the command window CW is used.

The command window CW includes a plurality of registers REGj (j=1,2, . .. , n) formed by volatile memory elements that are used for the purposeof receiving data to be written into, and commands to be executed onto,the memory matrix 200.

Particularly, each register REGj may absolve the function of trackingthe type of operation that is in execution (for example, programming orerasing), or may memorize the address RADD of the location(s) of thememory matrix 200 corresponding to the memory elements to which theoperation defined by the received command CMD is addressed. Furthermore,the registers REGj may be employed for storing the data to be writteninto the memory elements of the memory matrix 200. In addition, thecommand window CW may include one or more registers denoted “programbuffer” PB, usable in case the data to be written into the memory matrix200 in a single access are numerous.

As can be observed making reference to the FIG. 3, the command window CWis associated with a memory space that, if enabled, overlaps the memoryspace associated with the memory elements of the memory matrix 200. Inparticular, when the command window CW is activated (for example, by thememory controller 150), a base address BADD is set, indicative of theposition of the memory space associated with the command window CWwithin the whole memory space of the memory matrix 200. The base addressBADD corresponds to the particular row address RADD of the memory matrix200 starting from which the command window CW overlaps to the memoryspace associated with the memory matrix 200. The extent of such overlapdepends on the size of the memory space associated with the commandwindow CW, which depends, in turn, on the number of registers REGjforming the command window and by the size of the program buffer PB. Asit is shown in FIG. 3, varying such base address BADD it is possible tobring the command window CW to overlap to different zones of the memoryspace associated with the memory matrix 200.

When the memory matrix 200 is accessed for a writing operation, if theselected row address RADD is comprised within the memory space of thecommand window CW, the various phases that compose the writing operationinterest the content of the registers REGj of the command window CW,instead of the content of the memory elements of the memory matrix 200.

For this purpose, the selection block 215 checks the row address RADDand compares it with the base address BADD. If the row address RADDcorresponds to the memory space defined by the command window CW, theselection block 215 drives the selectors 205 in such a way to connectthe command window CW with the input/output terminal of the selector210, excluding thus the access to the memory matrix 200.

The writing operation that makes use of the command window CW starts ina way similar to that of the previous operations described in thepresent description, i.e., with a row opening phase started by thereception of an ACTIVE command sent by the memory controller 150. Theonly difference is that the selected row register RDBi is filled withthe content of one or more registers of the command window CW, insteadof with the content of a row of the memory matrix 200.

Afterward, one or more write access phases are performed, each startedby the reception of a corresponding WRITE command sent by the memorycontroller 150, and having the purpose of modifying portions potentiallydifferent of the content of the selected row register RDBi according tothe received column address CADD.

According to an embodiment of the present invention, the writingoperation ends with a phase denoted “closure and transfer phase” startedby the reception of a “FLUSH” command sent by the memory controller 150.

In order to start the closure and transfer phase, the memory controller150 sends onto the memory bus 140, together with the last command WRITEof the sequence, the command FLUSH, which signals to the DDR NVM 130 totransfer the content of the selected row register RDBj to the commandwindow CW—particularly, to one or more selected registers REGj of thecommand window, or to the program buffer PB. Thus, according to anembodiment of the present invention, such FLUSH command is issuedcontemporaneously with the last WRITE command of the sequence. Ingreater detail, for the FLUSH command it may used a bit, denoted flagbit FG, that is sent onto the address and command bus of the memory bus140 contemporaneously with the last WRITE command of the sequence.

The flag bit FG may be activated every time the content of the selectedrow register RDBi has to be transferred to the command window CW.

In greater detail, while during each writing access phase the datatransfer block 230 receives groups of bits that are used for updatingportions of the content of the selected row register RDBi (according tothe received column addresses CADD), the closure and transfer phase iscomposed by two sub-phases: a first sub-phase equal to a normal writingaccess phase, during which the data transfer block 230 receives a groupof bits sent with the last WRITE command of the sequence, to be used forupdating a last portion of the content of the row register RDBi, and asecond sub-phase in which, having retrieved the flag bit FG sent withthe last WRITE command, the content of the selected row register RDBi istransferred to the command window CW.

Advantageously, the flag bit FG, that instructs the memory 130 on thenecessity to automatically execute a transfer of the content of theselected row register into the command window, is transferred in thesame way as, according to the protocol for the DDR SDRAM memories, it istransferred the flag bit that instructs the DDR SDRAM memory of thenecessity to automatically execute the row closure operation after alast WRITE or READ command has been received. This allows tosubstantially exploit the same protocol provided for the DDR SDRAMmemories even for interact with the DDR NVM memory.

An example of how a writing operation making use of the command windowCW is carried out according to an embodiment of the present invention isshown in FIG. 4.

In particular, FIG. 4 shows a diagram that illustrates the evolution intime of the data and commands that flows on the memory bus 140 when theDDR NVM memory 130 carries out a writing operation composed by a writeaccess phase (triggered by a first WRITE command) directed to writeeight words or memory bytes bo, b1, . . . , b7, followed by a closureand transfer phase (triggered by the second and last WRITE commandsetting the flag bit FG) directed to write eight words or memory bytesb8, b9, . . . , b15, too. At the time instant t1 the memory controller150 sends onto the memory bus 140 the first WRITE command. At the timeinstant t9 the memory controller 150 sends onto the memory bus 140 thesecond and last WRITE command, together with the FLUSH command, i.e.,sends a WRITE command activating the flag bit FG. As a consequence, assoon as the last memory byte b15 is sent to the selected row registerRDBi (in this case, after the time instant t18), the transfer of thecontent of the row register RDBi to the command window CW is started.

According to an alternative embodiment of the present invention, theflag bit FG may be a dedicated bit of the memory bus 140, i.e., notnecessarily the flag bit that is used in the protocol of the DDR SDRAMmemories for automatically triggering the row closure operation, or oneof the available bits that are not used during the sending of the WRITEcommand from the address and command bus of the memory bus 140.

If the writing operation regards the updating of a single register REGj,it is sufficient to modify only a single portion of the content of therow register RDBi. Consequently, it is possible to execute the writingoperation by means of a single WRITE command (particularly, said WRITEcommand will be sent contemporaneously to the FLUSH command).

The transfer of the content of the selected row register RDBi to theregisters REGj and PB of the command window CW occurs with transferspeeds of the same order of those of a DDR SDRAM memory, since theregister REGj and PB of the command window are volatile registers, thatrequire shorts writing access times. In this way, it is possible toavoid all those problems due to the updating of the data stored in thenon-volatile elements of the memory matrix 200.

According to an embodiment of the present invention, during the datatransfer from the selected row register RDBi to the command window CW,every further WRITE or ACTIVE command generated by the memory controller150 is temporarily ignored by the DDR NVM memory 130. The possibility ofsending further commands to the DDR NVM memory 130 will be allowed assoon as the data transfer from the selected row register RDBi to thecommand window CW is concluded.

The content of the registers REGj and PB of the command window CW willbe transferred into the corresponding memory elements of the memorymatrix 200 in a subsequent time. This transfer occurs automatically andwithout the need of occupying the memory bus 140, which remains thusavailable for the execution of other operations.

It has to be underlined that, using the proposed solution, it ispossible to carry Out writing operations on the DDR NVM memory 130treating it substantially in the same way as of a DDR SDRAM memory,i.e., using substantially the same protocol used for managing theoperations of the DDR SDRAM memory 120.

Indeed, thanks to the presence of the command window CW, the timesemployed for writing the data into the DDR NVM memory 130 are of thesame order of magnitude of those used for writing the data into the DDRSDRAM memory 120.

Moreover, the transfer of the content of the row registers RDBi towardsthe command window CW is driven respecting the protocol that alreadyexists for the writing of the data into DDR SDRAM memories. Indeed,using the proposed solution, it is not necessary to use the memory bus140 for starting the closure operation and alter the protocol, since thetransfer is driven by means of the flag bit FG sent together with theWRITE command.

The command window CW may also be used during a reading operation, incase the selected row address RADD corresponds to the memory spacedefined by the command window. In this case, the reading operationoccurs in the same way as that previously described, with the onlydifference that the data that have been read come from the commandwindow CW instead of from the memory elements of the memory matrix 200.

FIG. 5 illustrates a state diagram of the DDR NVM memory 130.

FIG. 6 is a timing diagram illustrative of the delays of the commandsCMD during writing operations of the DDR NVM memory 130.

Naturally, in order to satisfy local and specific requirements, a personskilled in the art may apply to the solution described above manymodifications and alterations. Particularly, although the presentinvention has been described with a certain degree of particularity withreference to the described embodiments thereof, it should be understoodthat various omissions, substitutions and changes in the form anddetails as well as other embodiments are possible. Moreover, it isexpressly intended that specific elements and/or method steps describedin connection with any disclosed embodiment of the invention may beincorporated in any other embodiment as a general matter of designchoice.

For example, although in the description it has been explicitly madereference to a DDR NVM memory of the flash type, nothing prevents toemploy the proposed solution with other types of non-volatile memories,such as EPROM, PCM and so on.

Moreover, even if the present solution has been described as adapted tobe employed for devices with limited resources, such as the mobileterminals, similar considerations can be applied to any electronicsystem that needs both a non-volatile DDR memory and a volatile DDRmemory, or other volatile and non-volatile memories having a differentcommunications protocol.

Even if in the description reference has not been made explicitly to thespecific memory bus used by the memory system, the concepts of thepresent invention are applicable to different bus types, like the DDRbuses and the DDR2 buses mentioned herein as well as othercommunications protocols or bus types.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention.

What is claimed is:
 1. A method of writing data to a memory device, themethod comprising: buffering data in a first memory space; modifying thebuffered data responsive to receiving a command including a flushportion; based on a determination that the flush portion of the commandis active, storing the modified buffered data in a second memory space;and writing at least portions of the modified buffered data from thesecond memory space to the first memory space.